The present invention relates to a nonflammable building material comprising calcium silicate as the base material and to a process for preparing the same.
It has been common practice to prepare nonflammable building materials by a so-called dry process comprising the steps of mixing together an aggregate, cement and siliceous sand, admixing asbestos with the mixture as reinforcing fiber to obtain a starting material, spreading the starting material in the form of a layer on a belt conveyor, applying water to the material layer to cause the water to penetrate into the layer, shaping the layer by compression and curing the shaped material. When the starting material contains cement and siliceous sand in such amounts that the mole ratio of the lime component of the cement to the siliceous component of the siliceous sand (CaO/SiO.sub.2) is 0.5 to 1.0, further contains 20 to 60% by weight of aggregate and is cured in an autoclave with use of high-temperature steam of increased pressure, a building panel is obtained which possesses high strength and has tough calcium silicate crystals formed therein as is already known.
However, when the nonflammable building material thus produced is used for a prolonged period of time, the material is gradually subjected to weathering and abrasion, releasing fragments of the asbestos component. Such fragments will lodge in the respiratory organs of the human body and adversely affect one's health. Accordingly it has been desired to provide nonflammable building materials without using asbestos for reinforcement.
Further in recent years, asbestos has become expensive and extremely difficult to obtain and use owing to exhaustion of resources, so that attempts are made to use other fibers in place of asbestos or to dispense with asbestos.
Asbestos imparts various properties to nonflammable building materials. Needless to say, it gives improved strength to cured building materials. In the case where such building materials are prepared by the dry process, asbestos serves to promote penetration of water into the starting material and to prevent an uncured material from cracking when it is transferred from the belt conveyor to the subsequent process in the form of a panel.
Accordingly other fibers, if useful as substitutes for asbestos, must fully fulfill these functions.
Although it has been attempted to use glass fiber for the dry process in place of asbestos, which has too smooth a surface, is liable to slip off from uncured panels and is not fully effective in reinforcing the uncured panels. Glass fiber also fails to afford an effective capillary action to cause water to penetrate into the layer of starting material.